topic Re: Rotational speed of disk in Operating System - HP-UX

Rotational speed of disk

Christian S. Poulsen — Thu, 10 Aug 2000 09:54:31 GMT

Hi

Last night I experienced a disk problem on a K460, one of the disks started rotating very slowly, which also made the server respond very slowly.

Now, my question is, does any of you know a command in HP-UX 10.20 which dynamically can return me the rotational speed (RPM) of a disk?

Thanks in advance

/Christian

Re: Rotational speed of disk

Stefan Farrelly — Thu, 10 Aug 2000 09:53:45 GMT

Im not sure how you were able to tell that a disk was rotating slowly ?

But, to find out the speed of your disks find out the model number (ioscan -fkCdisk)
then take the value in the description field and go to the disks manufacturers site, eg. seagate.com, do a search there for the model, eg. ST32550N and it will give you the RPM.

Re: Rotational speed of disk

Andy Monks — Thu, 10 Aug 2000 10:39:17 GMT

I'd have to agree with Stefan. Unless you take the top off the disc, you've no way of telling how fast it's rotating.

hp-ux can't tell such things, because only the disk knows how fast it's going, and therefore the only thing you can do, is to find out what the rotational speed is, by looking up the specs of the disc on the web

Re: Rotational speed of disk

Christian S. Poulsen — Thu, 10 Aug 2000 10:42:39 GMT

Actually it was an HP guy who told me that it was rotating to slowly.

I know how to get the factory RPM, I'm more interested in the value at any given time?

Re: Rotational speed of disk

Stefan Farrelly — Thu, 10 Aug 2000 11:50:54 GMT

Andy is right, there is no known tool ive ever heard of that will tell you currently how fast a disk is currently rotating - not on HP's anyway. If an HP guy told you it was spinning slowly then the only conceiveable way he could determine (guess) this was by being very close to the disk when it powers on and listening if it spins up fully. Well, if an HP guy said it then it must be faulty, get it replaced!

Re: Rotational speed of disk

Bill Hassell — Thu, 10 Aug 2000 13:04:15 GMT

Having been a part of a disk design team in years past, disks have only two speeds: stopped and full speed. Anything less than the nominal speed will cause the heads to fly closer to the disk, eventually touching the disk surface and after a while, scraping off the surface which flies around inside the housing. And a bit later, the particles get caught between the microinch distance between the head and disk and instantly, your data bits are now floating around randomly (ie, a head crash).

To determine the RPM of a disk would require a sensor, some logic to capture the sensor output and convert it to RPM, some non-std staus bits for the SCSI inquiry and some code to read the bits and report the result. With 20 Gb disks selling for less that $200 US, there is no incentive for RPM.

If the system seems slow, start with a reading of the man pages for sar, vmstat, iostat, top and determine whether the slowdown is due to a runaway application. Or you can save a lot of time and load Glance from your Application CDROMs.

Re: Rotational speed of disk

Dragan Krnic — Fri, 11 Aug 2000 06:54:17 GMT

With some exercise and fine tuning, it should be possible to calculate the rotational speed by measuring the read time for disk blocks (usually 512 bytes) from the same track and head. Consult manufacturer's specs for details on sectors/track, there are usually several zones with decreasing s/t numbers from outside towards inside of the disk.

However, as someone cleverly remarked, there is either full speed or full stop. Nothing in between.